Barbed metal insert overmolding using crosslinked polymers

ABSTRACT

The invention described herein relates to method by which a leak-proof connection may be made to a refrigeration device using shape memory characteristics of crosslinking and overmolding to affect the leak-proof connection.

RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 12/618,296 filed Nov. 13, 2009, now U.S. Pat. No. 8,220,126 B2the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The invention relates generally to a leak-proof method for securing afitting to a crosslinked polymeric tube, coupled with overmolding.

BACKGROUND OF THE INVENTION

Most refrigerators sold today have at least automatic ice makers andchilled water dispensers. In order to achieve the requisite water flowinto these devices, it is necessary to connect to a water supply line.This necessarily entails a connection between the water system in a homeor apartment or other building with the internal water conduits withinthe refrigeration device. Typically, this has entailed the use of hoseclamps or other connectors when the internal water conduits are made ofpolymeric tubes. However, hose clamps are labor-intensive to install andprone to leaks if not fastened tightly enough about the periphery of thepolymeric tube.

There is a need for a better connection between an inserted metallicconnector and the polymeric tube into which the connector is insertedwithout the need to resort to the use of hose clamps or othercircumferential fastening devices, such devices additionally useful asrisers or automotive tubes.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, there is provided anovermolding method in combination with crosslinked extruded polymerictubing and insertable connectors which remove the need for hose clampsfor circumferential compressive attachment.

In one embodiment of the invention, the process involves a process forsecuring a house water line to a water distribution system within arefrigeration device comprising the steps of: crosslinking at least aportion of a tube to set the permanent internal diameter of said tubeand shape memory characteristics in that portion; inserting a shaft of aconnector into the tube, an I.D. of the tube being equal to or smallerthan an O.D. of the shaft; and applying an external stimulus (e.g., atemperature in excess of the transition temperature T_(trans), or anelectric field, or a magnetic field, or light or a change in pH, etc.)or an internal stimulus (e.g., the passage of time) to at least theportion to contract the tube about the shaft, optionally withovermolding a polymeric attachment means onto the tube and/or connectorat or adjacent one end of the tube and about at least a portion of thetube and/or connector where it is crosslinked. The step of crosslinkingis generally between 20-98% crosslinking, more preferably between 40-90%crosslinking, and most preferably between 65-89% crosslinking. At leastthe shaft of the connector is metallic and preferably has raisedretention means, e.g., laterally-extending ribs and raised barbs. Themetallic portion is preferably brass or stainless steel.

In another embodiment of the invention, the process involves a processfor securing a house water line to a water distribution system within arefrigeration device comprising the steps of: overmolding a polymericattachment means onto a tube at or adjacent one end of the tube, acomposition of the overmolded polymeric attachment means being at leastpartially chemically compatible with the tube; crosslinking at least aportion of the tube and the attachment means to set a permanent internaldiameter of the tube and shape memory characteristics in that portion;inserting a shaft of a connector into the tube, an I.D. of the tubebeing equal to or smaller than an O.D. of the shaft; and applying anexternal force (e.g., a temperature in excess of the transitiontemperature T_(trans), or an electric field, or a magnetic field, orlight or a change in pH, etc.) or an internal stimulus (e.g., thepassage of time) to at least the portion to contract said tube about theshaft.

In another embodiment of the invention, the process involves a processfor securing a house water line to a water distribution system within arefrigeration device comprising the steps of: crosslinking at least aportion of a tube to set a permanent internal diameter of said tube andshape memory characteristics in that portion; inserting a shaft of aconnector into the tube, an I.D. of the tube being equal to or smallerthan an O.D. of the shaft; overmolding a polymeric attachment means ontothe tube at or adjacent one end of the tube and about at least a portionof the tube which is crosslinked, the polymeric attachment means notforming a material-to-material bond with the tube; and applying anexternal force (e.g., a temperature in excess of the transitiontemperature T_(trans), or an electric field, or a magnetic field, orlight or a change in pH, etc.) or an internal stimulus (e.g., thepassage of time) to at least the portion to contract the tube about theshaft.

These and other objects of this invention will be evident when viewed inlight of the drawings, detailed description, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a tube with overmolded end sectionwithout the insertion of a metallic fitting;

FIG. 2A is a perspective view of a barbed metallic fitting with internalthreads at one end;

FIG. 2B is a side elevational view in cross-section of an externallythreaded barbed metallic fitting;

FIG. 3 is a perspective view of the tube with overmolded end section ofFIG. 1 with inserted barbed metallic fitting of FIG. 2 b with watersupply line attached;

FIG. 4 is a perspective view of the barbed metallic fitting of FIG. 2 binserted into a crosslinked polymeric tube;

FIG. 5 is a perspective view of FIG. 4 with overmolded end section;

FIG. 6A is a flow diagram of a processing sequence for the invention;

FIG. 6B is another embodiment of a flow diagram of a processing sequencefor the invention;

FIG. 7 is a side elevational view in cross-section illustrating a barbedmetallic fitting inserted into a crosslinked tube;

FIG. 8 is a side elevational view of FIG. 7 in cross-sectionillustrating the split heating blocks positioned about the crosslinkedtube with inserted barbed fitting;

FIG. 9 is a side elevational view of FIG. 8 in cross-section after thesplit heating blocks have been closed;

FIG. 10 is a perspective view of a tube with an alternative overmoldedend portion without the insertion of a metallic fitting; and

FIG. 11 is a cross-sectional view through the overmolded end section ofFIG. 10 with a fitting inserted in the overmolded end portion.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to the drawings wherein the showings are for purposes ofillustrating the preferred embodiment of the invention only and not forpurposes of limiting the same, the Figures show a leak-proof method ofconnection with a metallic connector and a crosslinked polymeric tube.

FIG. 1 shows an extruded polymeric tube 12 about which is overmoldedattachment piece 46 as it might be configured for installation onto arear panel of a refrigeration device (not shown). Attachment piece 46has a top and a bottom face 24 and a pair of opposed wings 18, at leastone of which has aperture 20 extending therethrough. Each face has anaperture 36 disposed therein, the I.D. (“Internal Diameter”) of theaperture closely approximates the O.D. (“Outer Diameter”) of polymerictube 12.

As better illustrated in FIGS. 2A and 2B, connector 50 a or 50 b may beinserted into the I.D. of polymeric tube 12. Connector 50 a is aninternally threaded fitting illustrated in FIG. 2A while connector 50 bis an externally threaded fitting illustrated in FIG. 2B. Eitherconnector is typically made of metal, although it is possible that withthe addition of various fillers (e.g., glass-filled) and/or judiciouschoice of polymer composition, selected polymers may be employed in theapplication. Either connector has a front face 16, a beveled rear face34, plurality of threads 22, hexagonal (or other integral number of) nutfaces 28, and shaft 32 with preferably at least one outwardly-extendingor laterally-extending rib or barb 30.

As illustrated in FIG. 4, upon insertion of either connector 50 a (notshown) or connector 50 b (illustrated), with the geometry of the O.D. ofconnector shaft 32 being at least equal to the I.D. of polymeric tube12, preferably the relationship of the O.D. of connector shaft 32 isgreater than the I.D. of polymeric tube 12, laterally-extending ribs 30produce a deformation of polymeric tubing wall 12. In a most preferredembodiment, the I.D. of polymeric tubing 12 is fixed to a smallerdimension than the O.D. of shaft 32 of connector 50 a or 50 b bycrosslinking prior to insertion of any connector. Crosslinking imparts a“memory” to the polymeric tubing's original dimensions, and upondeformation of the same, will tend to resort back to the originaldimension when crosslinked upon the application of a transforming forcein a manner described later in the application. Using this shape-memoryfeature permits leak-proof engagement of the peripheral circumferentialwalls of shaft 32 with associated laterally-extending ribs 30 to secureleak-proof engagement with the inner walls of polymeric tubing 12. Thisis particularly preferable when the polymeric walls are polyethylene,which when crosslinked become crosslinked polyethylene or “PEX.”

FIG. 5 illustrates the assembled connector 10 after overmolding. Theovermolding in the figure illustrates the overmold extending beyond aportion of the encapsulated faces of nut 28 in addition to extendingbelow the encapsulated faces and upon at least a portion of polymerictubing 12. Preferably, the overmold continues to extend over at leastone retention means, e.g., laterally-extending rib 30 or raised barb.FIG. 6 illustrates a completed connector of the present invention afterjoining with water supply line 38 by threaded nut 40.

In processing, as illustrated in FIGS. 6A and 6B, there are twodifferent methods which may be employed in the invention. In the seriesof steps illustrated in FIG. 6A, a manufacturer would extrude a polymerusing traditional extrusion technologies, and cut the extruded tubing toa desired length. In this sequence, the extrudate is overmolded,followed by crosslinking and ultimately, insertion of the componentfitting into the crosslinked extrudate. In the series of stepsillustrated in FIG. 6B, a manufacturer would extrude a polymer and cutthe extruded polymer to a desired length as described with FIG. 6A,followed by crosslinking, fitting insertion and ultimately, overmolding.It has been found that when practicing the process illustrated in FIG.6B, that the step of overmolding not form a material-to-material bond(or if such bond forms, it is a weak bond) with the exterior ofpolymeric tubing 12. In this manner, the overmold acts as a separatemember and allows the tube to move independently of the overmold. Commonto both processes is the fact that the step of crosslinking precedes thestep of insertion of the component fitting. In the process illustratedin FIG. 6B, when the step of crosslinking precedes the overmolding step,illustrative overmolding polymers would be glass-filled polypropylene,which cannot be irradiated in that polypropylene degrades under theapplication of an electron beam. However, polypropylene has higher heatdistortion properties, and provides a better clamp in the applicationwhen compared to glass-filled polyethylene. With unfilled polyethylene,it is possible to overmold onto the tube, and then beam both the tubeand overmold as one unit.

As used in this application, the term “overmold” means the process ofinjection molding a second polymer over a first polymer, wherein thefirst and second polymers may or may not be the same. In one embodimentof the invention, the composition of the overmolded polymer will be suchthat it will be capable of at least some melt fusion with thecomposition of the polymeric tube. There are several means by which thismay be affected. One of the simplest procedures is to insure that atleast a component of the polymeric tube and that of the overmoldedpolymer is the same. Alternatively, it would be possible to insure thatat least a portion of the polymer composition of the polymeric tube andthat of the overmolded polymer is sufficiently similar or compatible soas to permit the melt fusion or blending or alloying to occur at leastin the interfacial region between the exterior of the polymeric tube andthe interior region of the overmolded polymer. Another manner in whichto state this would be to indicate that at least a portion of thepolymer compositions of the polymeric tube and the overmolded polymerare miscible. The process of FIG. 6A illustrates the term “overmolding”with chemical compatibility. However, the process of FIG. 6B illustratesthe term “overmolding” without chemical compatibility. In other words,the chemical composition of the polymers is relatively incompatible,thereby not resulting in a material-to-material bond after the injectionovermolding process.

In one embodiment of this invention, polymeric tubing 12 is made fromhigh density polyethylene which is crosslinked. PEX contains crosslinkedbonds in the polymer structure changing the thermoplastic into athermoset. Crosslinking may be accomplished during or after the moldingof the part. The required degree of crosslinking for crosslinkingpolyethylene tubing, according to ASTM Standard F 876-93, is between65-89%. There are three classifications of PEX, referred to as PEX-A,PEX-B, and PEX-C. PEX-A is made by the peroxide (Engel) method. In thePEX-A method, peroxide blended with the polymer performs crosslinkingabove the crystal melting temperature. The polymer is typically kept athigh temperature and pressure for long periods of time during theextrusion process. PEX-B is formed by the silane method, also referredto as the “moisture cure” method. In the PEX-B method, silane blendedwith the polymer induces crosslinking during molding and duringsecondary post-extrusion processes, producing crosslinks between acrosslinking agent. The process is accelerated with heat and moisture.The crosslinked bonds are formed through silanol condensation betweentwo grafted vinyltrimethoxysilane units. PEX-C is produced byapplication of an electron beam using high energy electrons to split thecarbon-hydrogen bonds and facilitate crosslinking.

Crosslinking imparts shape memory properties to polymers. Shape memorymaterials have the ability to return from a deformed state (e.g.temporary shape) to their original crosslinked shape (e.g. permanentshape), typically induced by an external stimulus or trigger, such as atemperature change. Alternatively or in addition to temperature, shapememory effects can be triggered by an electric field, magnetic field,light, or a change in pH, or even the passage of time. Shape memorypolymers include thermoplastic and thermoset (covalently crosslinked)polymeric materials.

Shape memory materials are stimuli-responsive materials. They have thecapability of changing their shape upon application of an externalstimulus. A change in shape caused by a change in temperature istypically called a thermally induced shape memory effect. The procedurefor using shape memory typically involves conventionally processing apolymer to receive its permanent shape, such as by molding the polymerin a desired shape and crosslinking the polymer defining its permanentcrosslinked shape. Afterward, the polymer is deformed and the intendedtemporary shape is fixed. This process is often called programming. Theprogramming process may consist of heating the sample, deforming, andcooling the sample, or drawing the sample at a low temperature. Thepermanent crosslinked shape is now stored while the sample shows thetemporary shape. Heating the shape memory polymer above a transitiontemperature T_(trans) induces the shape memory effect providing internalforces urging the crosslinked polymer toward its permanent orcrosslinked shape. Alternatively or in addition to the application of anexternal stimulus, it is possible to apply an internal stimulus (e.g.,the passage of time) to achieve a similar, if not identical result.

A chemically crosslinked network may be formed by low doses ofirradiation. Polyethylene chains are oriented upon the application ofmechanical stress above the melting temperature of polyethylenecrystallites, which can be in the range between 60° C. and 134° C.Materials that are most often used for the production of shape memorylinear polymers by ionizing radiation include high density polyethylene,low density polyethylene and copolymers of polyethylene and poly(vinylacetate). After shaping, for example, by extrusion or compressionmolding, the polymer is covalently crosslinked by means of ionizingradiation, for example, by highly accelerated electrons. The energy anddose of the radiation are adjusted to the geometry of the sample toreach a sufficiently high degree of crosslinking, and hence sufficientfixation of the permanent shape.

Another example of chemical crosslinking includes heating poly(vinylchloride) under a vacuum resulting in the elimination of hydrogenchloride in a thermal dehydrochlorination reaction. The material can besubsequently crosslinked in an HCl atmosphere. The polymer networkobtained shows a shape memory effect. Yet another example is crosslinkedpoly[ethylene-co-(vinyl acetate)] produced by treating the radicalinitiator dicumyl peroxide with linear poly[ethylene-co-(vinyl acetate)]in a thermally induced crosslinking process. Materials with differentdegrees of crosslinking are obtained depending on the initiatorconcentration, the crosslinking temperature and the curing time.Covalently crosslinked copolymers made from stearyl acrylate,methacrylate, and N,N′-methylenebisacrylamide as a crosslinker.

Additionally shape memory polymers include polyurethanes, polyurethaneswith ionic or mesogenic components, block copolymers consisting ofpolyethyleneterephthalate and polyethyleneoxide, block copolymerscontaining polystyrene and poly(1,4-butadiene), and an ABA triblockcopolymer made from poly(2-methyl-2-oxazoline) andpoly(tetrahydrofuran). Further examples include block copolymers made ofpolyethylene terephthalate and polyethylene oxide, block copolymers madeof polystyrene and poly(1,4-butadiene) as well as ABA triblockcopolymers made from poly(tetrahydrofuran) andpoly(2-methyl-2-oxazoline). Other thermoplastic polymers which exhibitshape memory characteristics include polynorbornene, and polyethylenegrated with nylon-6 that has been produced for example, in a reactiveblending process of polyethylene with nylon-6 by adding maleic anhydrideand dicumyl peroxide.

FIGS. 7-9 are illustrative of one manner of employing shape memorycharacteristics of polymer tube 12 about barbed shaft 30 of a connector.FIG. 7 illustrates the insertion of beveled end 34 of the shaft into theI.D. of the tubing in a highly stylized manner. FIG. 8 illustrates theapplication of a split mold 42 a, 42 b with corresponding internal moldvoids 44 which are positionable about protruding barbs 30 of the shaftof the connector. In this example as illustrated in FIG. 9, theapplication of heat induces the shape memory polymer to induce the shapememory effect by exceeding transition temperature T_(trans).

FIG. 10 shows an alternative overmolded attachment piece 46′ overmoldedonto an extruded polymeric tube 12′, the overmolded attachment piece 46′having a bore 52 in fluid communication with the I.D. of the tube 12′.As shown by the example in FIG. 11, the connector 50 a (not shown) orconnector 50 b (illustrated) may be inserted into the bore 52. In theembodiment of FIG. 11, the geometry of the O.D. of connector shaft 32 isat least equal to the I.D. of the bore 52, and preferably therelationship of the O.D. of connector shaft 32 is greater than the I.D.of the bore 52. Upon insertion of either connector 50 a or connector 50b, the laterally-extending ribs 30 produce a deformation of theovermolded attachment piece 46′ around the bore 52. In a most preferredembodiment, the I.D. of the bore 52 is fixed to a smaller dimension thanthe O.D. of shaft 32 of connector 50 a or 50 b by crosslinking prior toinsertion of any connector. The connector 50 a or 50 b may be insertedinto the bore 52 without being inserted into the I.D. of polymeric tube12′ as shown in FIG. 11.

As discussed above, the shape memory of crosslinking provides internalforces urging the crosslinked overmolded attachment piece 46′ toward itsoriginal dimensions after deformation of the same. When the connector 50a or 50 b having an outer diameter larger than the original dimensionsof the bore 52 of the attachment piece 46′ is placed into the bore, theshape memory property of the polymer cannot fully revert to its originaldimensions, but draws at least partially toward its original dimensionaround the connector. The shape memory of crosslinking enables theovermolded attachment piece 46′ to engage the peripheral circumferentialwalls of the shaft 32, and the overmolded attachment piece may conformto at least a portion of the shape of the shaft 32. Using theshape-memory of the crosslinked attachment piece permits leak-proofengagement of the peripheral circumferential walls of the shaft 32 toform a leak-proof engagement with the inner walls of the bore 52. Thecrosslinked attachment piece 46′ may engage the peripheralcircumferential walls of the shaft 32 with or without the application ofheat as discussed above with reference to FIGS. 7-9. In certainapplications, the overmolded attachment piece 46′ is crosslinkedpolyethylene or “PEX.”

As used in this application, crosslinking percentages which range from20-98% are applicable, with a more preferred range being 40-90%, andmost preferred from 65-89%.

While a threaded connector (internally threaded or externally threaded)is illustrated in the figures, this is not a requirement of theinvention, although preferred for the water connection to arefrigeration device. For some applications, the geometry on the side ofthe connector which is opposite the barbed end, the geometry could bedifferent, such as for example as appropriate to a “push-to-connect”fitting with zero threads.

While a barbed connector shaft is illustrated in this application, ifthe geometries of the tubing and the connector are appropriate, andsufficient frictional force is required to insert the connector into thefitting, no barbs may be necessary.

As used in this application, the requisite degree of I.D. tubingexpansion by the inserted connector is between at least approximately 5%and 100% inclusive, the degree of expansion dependent upon variousfactors, including the wall thickness of the tube, the thicker the wall,the less I.D. expansion typically employed. The I.D. expansion is alsorelated to wall thickness, and this percentage can range from at leastapproximately 20% to 150% inclusive, this percentage increases as wallthickness decreases. In a more preferred embodiment, the requisitedegree of I.D. tubing expansion by the inserted connector will beincreased by an amount which corresponds to a radial height of a barb,which typically ranges approximately an additional 5%, more preferably10%, most preferably 15% in addition to the expansion achieved byfitting insertion. Of course it is recognized that if the insertedconnector expands the I.D. of the tubing by a sufficient degree, and theamount of insertion is sufficient to impart a surface area which createslateral forces in excess of any internal water pressure, i.e.,F_((lateral retaining force))>F_((house water pressure)) then no barbsare necessary, although highly preferred. While house water pressure isthe comparative useful for the disclosed application, in a more genericsense, the relationship must simply exist in comparison to the intendedapplication.

While tubing 12 is preferably imparted with shape memory characteristicsthroughout the entire length of tubing used, there is no need to limitthe invention to such. In fact, only the portion of the tubing intowhich shaft 32 of either connector 50 a or connector 50 b is required tohave shape memory characteristics.

While tubing 12 is preferably circular, other profiles are envisioned tobe within the scope of this invention, although circular I.D. profilesare most often encountered. The invention is additionally not limited tohouse water line connections to water distribution systems withinrefrigeration devices, but rather encompasses all manner of tubingconnections, including any fluid (whether liquid or gaseous).

The best mode for carrying out the invention has been described for thepurposes of illustrating the best mode known to the applicant at thetime. The examples are illustrative only and not meant to limit theinvention, as measured by the scope and spirit of the claims. Theinvention has been described with reference to preferred and alternateembodiments. Obviously, modifications and alterations will occur toothers upon the reading and understanding of the specification. It isintended to include all such modifications and alterations insofar asthey come within the scope of the appended claims or the equivalentsthereof.

What is claimed is:
 1. A process for securing a water conduit to anotherwater conduit comprising the steps of: overmolding a polymericattachment means having a bore onto a tube at or adjacent one end ofsaid tube; crosslinking at least a portion of said tube and saidattachment means setting a permanent internal diameter of said bore andshape memory characteristics in said portion; inserting a shaft of aconnector into said bore, an inside diameter of said bore being equal toor smaller than an outside diameter of said shaft; and applying anexternal or internal stimulus to at least said portion to contract saidbore about said shaft.
 2. The process of claim 1 wherein said externalstimulus is a temperature in excess of a transition temperature(T_(trans)).
 3. The process of claim 1 wherein said internal stimulus istime.
 4. The process of claim 1 wherein said step of crosslinking saidtube is between 20-98% crosslinking.
 5. The process of claim 4 whereinsaid step of crosslinking said tube is between 40-90% crosslinking. 6.The process of claim 3 wherein said step of crosslinking said tube isbetween 65-89% crosslinking.
 7. The process of claim 1 wherein saidshaft of said connector is metallic and further comprises raisedretention means.
 8. The process of claim 7 wherein said shaft isselected from the group consisting of stainless steel and brass; andsaid retention means is selected from the group of laterally-extendingribs and raised barbs.
 9. A process for securing a fitting into apolymeric profile comprising the steps of: overmolding a polymericattachment means having a bore onto a profile at or adjacent one end ofsaid profile; crosslinking at least a portion of said profile and saidattachment means setting a permanent internal diameter of said bore andshape memory characteristics in said portion; inserting a shaft of aconnector into said bore, an inside diameter of said bore being equal toor smaller than an outside diameter of said shaft; and applying anexternal or internal stimulus to at least said portion to contract saidbore about said shaft.
 10. The process of claim 9 wherein said externalstimulus is a temperature in excess of a transition temperature(T_(trans)).
 11. The process of claim 9 wherein said internal stimulusis time.
 12. The process of claim 9 wherein said step of crosslinkingsaid profile is between 20-98% crosslinking.
 13. The process of claim 12wherein said step of crosslinking said profile is between 40-90%crosslinking.
 14. The process of claim 13 wherein said step ofcrosslinking said profile is between 65-89% crosslinking.
 15. Theprocess of claim 9 wherein said shaft of said connector is metallic andfurther comprises raised retention means.
 16. The process of claim 15wherein said shaft is selected from the group consisting of stainlesssteel and brass; and said retention means is selected from the group oflaterally-extending ribs and raised barbs.
 17. The process of claim 9wherein said profile is a tube.